Multiplex PCR-detected sexually transmitted infections are associated with increased seminal oxidative stress and impaired semen quality in infertile men.

Sexually transmitted infections (STIs), including Chlamydia trachomatis and Neisseria gonorrhoeae, as well as emerging pathogens such as Mycoplasma genitalium and Ureaplasma spp., have been implicated in male reproductive dysfunction through inflammatory and oxidative stress-mediated mechanisms. However, the clinical significance of infections detected by multiplex polymerase chain reaction (PCR) remains to be fully elucidated. This retrospective cross-sectional study examined the association between STIs identified by a 14-target multiplex PCR panel, seminal oxidative stress assessed by oxidation-reduction potential (ORP), and semen quality in infertile men. A total of 153 men undergoing infertility evaluation between June 2023 and June 2025 were included. Semen analysis was performed according to the World Health Organization (WHO) 2021 guidelines. STI pathogens were detected using multiplex PCR, and oxidative stress was measured using the MiOXSYS system. Associations were evaluated using generalized linear models and ANCOVA adjusted for age, body mass index, smoking, alcohol consumption, and infertility duration. STIs were detected in 32.0% of participants, including single infections in 22.9% and multiple infections in 9.1%. Overall STI positivity was not significantly associated with conventional semen parameters or ORP levels. However, multiple infections were associated with a higher likelihood of elevated ORP (OR 1.96, 95% CI 0.60-6.41), and inflammation-associated pathogens showed a similar trend (OR 2.05, 95% CI 0.73-5.82). Men with both STI infection and elevated ORP demonstrated significantly reduced progressive motility, sperm concentration, and normal morphology compared with STI-negative men with normal ORP (all P < 0.001). These findings suggest that infection burden combined with oxidative imbalance, rather than STI positivity alone, may contribute to sperm dysfunction. Integrating molecular STI screening with oxidative stress assessment may improve the biological evaluation of male infertility.